The geometric design, especially the horizontal and vertical alignments, of rural two-lane
highway facilities is considered one of the most important factors affecting the quality of
traffic service and safety. A consistent highway geometric design is defined to be one that
conforms to the driver's expectations. In order to calculate the main measures of design
consistency, an accurate operating speed profile model for road alignment is needed.
Studies have shown that operating speed models are country dependent due to varying
demographics, driver attitudes, habits, etc. This paper develops a speed profile model for
two-lane rural roads in Egypt. This includes the development of operating speed models for
horizontal curves and tangents, as well as the study of the characteristics and relationships
between acceleration and deceleration rates before and after horizontal curves. The study
uses a desert rural two-lane, two-way road sections that connect the city of Sohag with the
city of Hurghada, in Upper Egypt. All geometric characteristics were obtained from highway
authority. Speed data regarding individual drivers traveling on selected two-lane rural
road sections were sampled using an on-board GPS system. The study confirms the finding
in previous research that curvature is the most important factor in determining the speed
on horizontal curves. Moreover, tangent length is the most important factor in determining
operating speeds at tangents. The acceleration and deceleration characteristics were
derived to gain an understanding of the behavior of individual vehicles traveling through
curves of varying radii and lengths as well as preceding tangent length. Several operating
speed models were developed for tangents and curves as well as for acceleration and
deceleration rates. Incredibly effective, these models can be used for design consistency
evaluations.